Yes, Braga and Guimarães are easily reachable from Porto (direct train connections for both), but only doable if you spend at least a couple of nights in Porto.
From Lisbon, I’d recommend Tomar, which I love, but also Óbidos or Peniche, for example. From Peniche, you can take a boat to the Berlengas archipelago, which I’d say is more interesting than Peniche itself. And on your way to Peniche, you can also visit the quirkiest garden in Portugal, the Bacalhôa Buddha Eden, in Bombarral.
If you go a bit south, you have Arrábida (just don’t try driving to the most popular beaches in June, since private cars are not allowed to circulate during the beach season - use the free buses) and the Tróia peninsula, which is reachable by ferry from Setúbal. I don’t love Setúbal and I also don’t love Sesimbra (also relatively close and well known), but many tourists, both national and international, enjoy visiting them. Even further south, but hard to reach without a car, you have Badoca Safari Park, which is ten times better than a zoo, including for the animals themselves, I think (and hope).